Transformer construction



Jan. 15, 1952 J. G. SOLA 2,582,291

TRANSFORMER CONSTRUCTION Filed Aug. 5, 1948 2 SHEETS-SHEET l IN V ENTOR.

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Jan. 15, 1952 J. G. SOLA 2,582,291

TRANSFORMER CONSTRUCTION File'd Aug. -5, 1948 2 SHEETSSHEET 2 INVENTOR.\27 Joseph 6. 801a Gif 5 Patented Jan. 15,1952

UNITED srA'ras PATENT OFFICE TRANSFORMER CONSTRUCTION Joseph G. Sola,River Forest, Ill. Application August 5, 1948, Serial No. 42,646 aClaims. (01. 175-356) This invention relates to transformers of thepressed-in core type, more particularly to such transformerconstructions and methods for reducing noise or hum therein.

Transformers for supplying voltage to lamps of the discharge varietysuch as fluorescent lamps, for example, must be as free from hum aspossible, particularly in areas where the the noise level is low, as inbusiness ofilces.

Transformers of the pressed-in core type are disclosed in two formsrespectively in Patent No.

2,346,621, to Joseph G. 8012., for Alternating Current Supply System,and the application Ser. No. 15,701 of Joseph G. Sola, for Transformer,and the core of each transformer includes an outer leg or shell and aninner leg pressed into the shell. These transformers have been subjectto a certain amount of hum. In transformers of the character disclosedin the aforementioned application, where the stray field has beenlargely eliminated and thus the noise consequent thereto, some slighthum has remained. It has been determined that this residual hum is duelargely to the fact that all parts of the core did not lie in the sameplane. Due to magneto-strictive effects, the interaction of the magneticfields in the different parts of the core or for other reasons, the coreparts tend to vibrate relative to each other which causes humming.

Accordingly, it is a further object of the invention to provide animproved transformer having a, pressed-in type 'core wherein therelative vibration between the various parts of the core is eliminated.

While in the patent and application referred to the transformersdisclosed have been shown with fluorescent lamps and operate uponprinciples utilizing resonant circuits, and the present inventionrelates to transformers of this character, it has application as well topressed-in core type transformers generally.

In carrying out the invention in one form, a transformer is providedhaving a core formed of two parts. The outer part is made oflaminations, whose periphery is continuous, stacked together. The innerpart is made of laminations stacked together and having a lengthsomewhat less than the distance between the surfaces of the outer partwhich cooperate with the ends of the inner part. The metallic contactfor completing the magnetic circuit is made through the sides of theinner part rather than through the ends.

For a more complete understanding of the invention, reference should behad to the accompanying drawings, in which:

Figure 1 is a top view of one form of well-known transformer notembodying the invention;

Fig. 2 is a sectional view taken substantially along lines 22 of Fig. 1;

Fig. 3 is a top view of a transformer embodying the invention;

Fig. 4 is a sectional view along lines 44 of Fig. 3;

Fig. 5 is an end view of the in Figs. 3 and 4; and

Fig. 6 is a top view of a transformer embodying a modified form of theinvention.

Referring to the drawings, there is shown in Figs. 1 and 2 a transformerincluding a core it having a primary coil II and two secondary coils l2and I3 thereon, substantially as shown in the application previouslyreferred to.

Core It may comprise a series of stacked onepiece or continuouslaminations forming an outer leg or shell l4 and a series of stackedI-shaped laminations forming an inner leg II. In order to have thenecessary metal-to-metal contact for a good magnetic circuit, thejunctions i6 and I1 between the inner leg and the outer leg must beclose. One manner of forming the laminations of outer shell I (outerlaminations) is to punch them from a stock of metal of suitablethickness and other dimensions. In this process the windows for thevarious coils are punched out and in the same or a separate step thecentral 1- shaped laminations are punched out along lines It and II.This latter step is a simple punching step with no attempt being made tochange the length of the I-shaped laminations.

The core is completed by assembling the requisite stack of laminationsfor outer shell H, by assembling for inner leg IS a stack of I-shapedlaminations previously punched out in the forming of laminations forouter shell I, and pressing the inner leg into the outer shell along thesame lines it and I! at which the I-shaped laminations were punched.Before pressing inner leg II in, the coils are placed thereon. TheI-shaped lamination punched from a particular outer lamination does notnecessarily lie within the lamination from which it was punched,inasmuch as in the assembling process the various laminations becomeshuilled.

Even though the I-shaped laminations forming inner leg ii are punchedfrom the outer laminations forming outer shell H to which the inner legis finally assembled, the inner leg does not lie in the same plane asthe outer shell. If an I- shaped lamination is punched from an outerlamination (say along lines l6, l1) and the I- shaped lamination isplaced within the outer lamination at the junctions It and I1, the I-shaped lamination does not lie flat but has a bow in it. Apparentlyduring the punching process the I-shaped lamination becomes somewhatlonger than the space from which it is punched. This may be due to aslight burr at the end of the lamination, or possibly the edge alongwhich the shearing took place is not perfectly perpentaken substantiallytransformer shown dicular to the main surface of the lamination, or itmay be that some slight elongation has taken place. In any event, when aseries of the I- shaped laminations formed as described are assembled toform inner leg l5 and this leg is then pressed into the outer shell l4formed of laminations as described, a very tight connection is formed atjunctions l6 and I1 and inner leg I5 bows outwardly a substantialdistance as may be seen best in Fig. 2. In this figure broken line H!indicates the plane of one side of outer shell M, and line |9 indicatesthe edge of inner leg I5 when the transformer is formed in the mannerdescribed.

The transformer as described has been found to have a certain amount ofhum, apparently due to the vibration of inner leg l5 relative to theouter shell l4.

Changes in linear dimensions occur when magnetic fields are applied dueto magnetostrictive effects. Thus, outer shell l4 and inner leg l5 maycontract and expand along their lengths as the flux therethrough varies,thereby causing the inner leg to bow outwardly still further from theposition shown in Fig. 2 or possibly allowing it to spring to thestraight-line position and even outwardly on the side opposite to linesI8 and |9 depending upon the strengths and phases of the fluxes withinthe various parts. It may also be that inner leg |5 instead of bowing orvibrating from one side to the other as a whole may vibrate in formhaving nodes intermediate the ends thereof. Irrespective of how innerleg |5 vibrates or the magnetic effects giving rise thereto, it has beenfound that the vibration and the incident noise may be prevented byconstructing the transformer in a manner illustrated in Figs. 3, 4 and5, which embody the invention in one form.

Referring to Figs. 3, 4 and 5, there is shown a transformer generallysimilar to that shown in Figs. 1 and 2 in that the core embodies anouter shell 2| and an inner leg 22 pressed into slots therewithin, coilsbeing assembled thereon as shown. This form of core is constructed oflaminations forming outer shell 2| (outer laminations) and I-shapedlaminations forming inner leg 22 wherein the I-shaped laminations arepunched from corresponding outer laminations. In the punching processthe windows for the coils are punched out, and as part of the same stepor as a separate step, the I-shaped laminations are punched out alonglines 23, 25, 21 and 28 at one end and corresponding lines at the other.The I-shaped laminations are then assembled to form inner leg 22 whichis pressed into a corresponding stack of laminations forming outer leg2| along the lines where punching took place. The I-shaped laminationsare punched, however, so that the length between the ends 23 and 24 ofinner leg 22 is less than the distance between adjoining edges 25 and 26of the outer punchings. The I-shaped lamination is sufficiently shorterso that a small air gap may exist between edges 23 and 25, and 24 and26. This ap need not be large but only sufficient so that when inner leg22 is pushed into the slots in outer shell 2|, the ends 23 and 24 d notpush outwardly against surfaces 25 and 26. Consequently, there is notendency for inner leg 22 to bow outwardly. Rather, inner leg 22 liesperfectly straight and within the planes defining the sides of outershell 2| substantially as shown in Fig. 4.

The necessary metal-to-metal contact for producing a good magneticcircuit is produced by having contact alOIlg the lines or sides 21 and28 at each end of inner leg 22. During the punching operation when themetal is sheared along lines 21 and 28, the width of the I-shapedpunchings comes out such that when reassembled to the outer shellmetal-to-metal contact is formed along the same surfaces 21 and 28. Thisis due to phenomena already alluded to in that a burr may form alongedges 21 and 28 or possibly some slight elongation occurs therebetween.In any event, when laminations are punched and assembled as described,good metal-to-metal contact is formed along edges 21 and 28, therebyforming the requisite good magnetic circuit.

In the form of transformer shown, the legs of the outer shell may formthe return path for flux generated in the inner leg, and thus sufficientarea of contact must be provided so as not to im pair the magneticcircuit. Accordingly, the width of the legs of the outer laminations issufficiently large so that the length of contact between the inner legand outer shell along both lines 21 and 28 is equal to the width of theinner leg. In the construction shown this necessitates that the legs ofthe outer shell be somewhat wider than the inner leg in order to leavethe strips of metal 29 and 3| for maintaining the continuous peripheryof the outer laminations.

The transformer shown being of the character described in theapplication referred to, increas ing the width of the outer punchings,as shown in Fig. 3, is advantageous in that certain stray field effectsare eliminated. In transformers where additional metal in the outer legis not desired, other constructions of course may be used and still havethe present invention embodied therein. Thus, for example, aconstruction of the form shown in Fig. 6 may be used. In this form ofthe invention the side legs of the outer laminations have the same totaltransverse dimension as the inner leg punchings, but the width of theside legs is less than that shown in Fig. 3. Otherwise, themodifications of Figs. 3 and 6 are the same. The construction of theends in Fig. 6 is such that strips of metal 29 and 3| remain to form thenecessary metallic support so that metal-to-metal contact is obtainedalong edges 21 and 28.

While particular embodiments of the invention have been shown, it willbe understood, of course, that the invention is not limited theretosince many modifications may be made, and it is, therefore, contemplatedby the appended claims to cover any such modifications as fall withinthe true spirit and scope of the invention.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

1. An electromagnetic device core having an outer shell comprising astack of continuous punchings, and an inner leg comprising a stack ofpunchings having at each end thereof longitudinal surfaces andtransverse surfaces, said shell stack having end members and sidemembers, said end members including slots having longitudinal surfacesand transverse surfaces, each end of said inner leg being within arespective one of said slots with corresponding longitudinal surfacesextending in the same direction and corresponding transverse surfacesextending in the same direction, characterized in that, the transversesurfaces of the ends of said inner leg are spaced away from thetransverse surfaces of the corresponding slots and the longitudinalsurfaces of the ends of said inner leg engage corresponding longitudinalsurfaces of said slots.

' 2. An electromagnetic device core having an outer shell comprising astack of continuous punchings, and an inner leg comprising a stack ofpunchings, said shell stack having end members and side members, saidend members each having a slot within each of which is a respective endof said inner leg, the longitudinal dimension of said inner leg definingan axis, said slots and the respective ends of said inner leg thereineach having adjacent longitudinal surfaces parallel to said axis, saidslots and the respective ends of said inner leg therein having ad-.iacent surfaces transverse to said axis, characterized in that, thecorresponding transverse surfaces of said slots and of the ends of saidinner leg are spaced from each other, and corresponding longitudinalsurfaces of said slots and of the ends of said inner leg engage eachother.

3. An electromagnetic device core having an outer shell comprising astack of continuous punchings, and an inner leg including a stack ofpunchings, said shell stack having end members and side members, saidend members each having a slot within each of which is a respective endof said inner leg, the longitudinal dimension of said inner leg definingan axis, said slots and the respective ends of said inner leg thereineach having adjacent longitudinal surfaces parallel to said axis, saidslots and the respective ends of said inner leg therein having adjacentsurfaces including components transverse to said axis, characterized inthat, the transverse components of the corresponding surfaces of saidslots and of the ends of said inner leg are spaced from each other, andthe corresponding longitudinal surfaces of said slots and of the ends ofsaid inner leg engage each other.

4. An electromagnetic device core having an outer shell comprising astack of continuous punchings, and an inner leg including a stack ofpunchings, said shell stack having end members and side members, saidend members each having a slot within each of which is a respective endof said inner leg, the longitudinal dimension of said inner leg definingan axis, said slots and the respective ends of said inner leg thereineach having adjacent longitudinal surfaces parallel to said axis, saidslots and the respective ends of said inner leg therein having adiacentsurfaces transverse to said axis, characteriaed in that, thecorresponding transverse surfaces of said slots and of the ends of saidinner ice are spaced from each other, and correspondl' longitudinalsurfaces of said slots and of the endsof said inner leg engage eachother, the area of engagement of said longitudinal surfaces at each endof said inner leg being substantiallyebdualtothecross-sectionalareaofsaidinner 6. An electromagnetic devicecore having an outer shell comprising a stack of continuous punchingshaving end members and side members, and an inner leg including astackof punchingasaid end members each having a slot within each ofwhich is a respective end of said inner leg, the longitudinal dimensionof said innerlegdeilninganaxis,saidslotsandthe.respective ends of saidinner leg therein each having; adjacent longitudinal surfaces parallelto said axis, said slots and the respective ends of said inner legtherein having adjacent surfaces transverse to said axis. characterisedin that.

- 6 said inner leg is less than the distance between the correspondingtransverse surfaces of said slots, and corresponding longitudinalsurfaces of said slots and the ends of said inner leg engage each other.

6. An electromagnetic device core comprising, an outer shell including astack of continuous punchings having end members and side members, andan inner leg including a stack of punchings, the longitudinal dimensionof said inner leg defining an axis, said end members each including asubstantially rectangular slot having side surfaces parallel to saidaxis and end surfaces perpendicular to said axis, said inner leg havingends including side surfaces parallel to said axis and end surfacesperpendicular to said axis, the said ends of said inner leg being withinrespective ones of said slots, the parallel side surfaces of said slotsand of the ends of said inner leg being in engagement, and the length ofsaid inner leg being less than the distance between the perpendicularsurfaces of said slots.

7. An electromagnetic device core comprising. an outer shell including astack of continuous punchings having end members and side members, andan inner leg including a stack of punchings, the longitudinal dimensionof said inner leg defining an axis, said end members each including asubstantially rectangular slot having side surfaces parallel to saidaxis and end surfaces perpendicular to said axis, said inner leg havingends including side surfaces parallel to said axis and end surfacesperpendicular to said axis, the said ends of said inner leg being withinrespective ones of said slots, the parallel side surfaces of said slotsand of the said ends of said inner leg being in engagement with eachother, the cross section of the said end members of said shell beinggreater than one-half of the cross section of said inner leg, the areaof engagement of said side surfaces of said inner leg with said slotsbeing substantially equal to the cross section of said inner leg, andthe length of said inner leg being less than the distance between theperpendicular surfaces of said slots.

8. A lamination layer for an electromagnetic device core comprising anouter punching continuous in periphery and having end members and sidemembers, and an inner punching, said end members each including asubstantially rectangular slot having longitudinal edges and transverseedges, said inner punching having longitudinal edges at its ends andtransverse edges at its ends, said inner punching Lving with each of itsends in a respective one of said rectangular slots, there being a gapbetween the transverse edges of said inner leg and the respective slotat each end of said inner leg, and the longitudinal edges of said innerpunching adiacent the ends thereof engaging the longitudinal edges ofsaid slots.

JOSEPH G. BOLA.

REFERENCES CITED The following references are of record in the file ofthis patent:

I UNITED STATES PATENTS Number

